DESCRIPTION (Applicant's abstract): Cryptococcus neoformans is an ubiquitous yeast which is the most common cause of fatal fungal infection in patients with AIDS. The respiratory tract is the portal of entry for this opportunistic infection. Pulmonary clearance is dependent on the ability of the host to mount a protective T cell-mediated inflammatory response in the lung. The recruitment and activation of monocytes is a hallmark of an effective pulmonary response to C. neoformans. Macrophages direct the outcome of the infectious challenge at two fundamental levels: 1) macrophages are the resident, initial cellular defense against C. neoformans; 2) macrophages elaborate cytokines which control the development and expression of specific T cell immunity orchestrating both the level and types of T cell cytokines produced in this response. Our proposed studies will focus on the signals required to activate macrophages and the cytokines "activated" macrophages produce to drive T cells to either a Tc1/Th1 or a Tc2/Th2 cytokine profile. Hypothesis: CD8 T cells generated in lung and hilar nodes during pulmonary C. neoformans infections produce chemokines and IFN-gamma early in the infection; these cytokines are crucial for recruiting and priming macrophages for IL-12 production and the development of protective Tc1 and Th1 responses. Second, we propose that protective CD8 T cells, which produce cytokines that recruit and activate macrophages, can be generated in CD4- depleted animals. The Specific Aims are: 1) Determine if the presence of CD8 T cell cytokines in macrophage recruitment and activation during a C. neoformans infection; 2) Determine if the presence of IFN-gamma early in the infection is crucial for IL-12 production and the development of a protective Tc1/Th1 response; 3) Determine in vitro if macrophage urokinase plasminogen activator (uPA) is required for C. neoformans-induced IL-12 production; 4) Determine in vivo the role of uPA in driving Tc1/Th1 polarization following a C. neoformans challenge. Our proposed experiments will use specific monoclonal antibodies to block cytokines and deplete cells, "knock out" mice that are homozygous -/-for the disruption of key genes and the transfer of defined cells into immunodeficient scid mice to define the essential requisites for effective in vivo antimicrobial immunity to C. neoformans. In aggregate, our in vivo experiments will suggest novel approaches to macrophage recruitment and activation during states of prolonged CD4 depletion.